Conventionally, a radial plunger pump having a motor has been provided within a motor housing with a shaft rotatably provided within a pump housing and driven by the motor. Further, pump portion was provided within the pump housing for sucking and discharging the fluid. This conventional pump 13 described in U.S. Pat. No. 4,201,521.
Such a conventional type of the pump, however, has the disadvantage that the fluid within the pump portion leaks toward the motor.
Therefore, the conventional type motor has a seal member provided between the pump housing and the motor housing for preventing the leakage of the fluid. Applicants have found, however, that the seal member provided between the motor housing and the pump housing cannot always seal. Thus, the fluid within the pump housing can leak toward the motor housing even though the seal member is provided.
Since the fluid within the pump housing is applied to the seal member, and since the pressure of the fluid within the pump housing is varied in accordance with the operation of the pump portion, the pressure applied to the seal member should vary and reduce to the negative pressure when the pump portion works. The pressure within the pump housing, on the other hand, increases more than atmospheric pressure when the pump portion stops to work.